Before going into music full-time Sommer, who had studied mathematics and physics in Braunschweig and Göttingen, was also a noted mathematician.[1] He served as the director of the Braunschweig University of Technology, where he taught mathematics, from 1875 to 1881.[2]

He was most successful as a composer for the theatre. Several of his operas used librettos based on fairy tales and were first produced at Brunswick: Der Nachtwächter (1865), Loreley (1891), Rübezahl und der Sackpfeifer von Neisse (1904), Riquet mit dem Schopf (1907) and Der Waldschratt (1912).Saint Foix, a one-act opera, was given at Munich in 1894 and Der Meermann at Weimar in 1896; Der Vetter aus Bremen (1865), Augustin (1898) and Münchhausen (1896–8) were not performed. His incidental music to Hans von Wolzogen's Das Schloss der Herzen (1891) was first performed in 1897 in Berlin, in concert form. He placed great importance on the literary quality of his librettos, and corresponded with numerous librettists and composers. His many songs, at one time known in England, include the cycles Der Rattenfänger von Hameln, Der wilde Jäger and Sapphos Gesänge; he also wrote orchestral works and male-voice choruses.

^John Alexander Fuller-Maitland -Masters of German Music 1894- Page 276 "When Richard Strauss was born, Hans Sommer was twenty-six years old, and yet he is properly to be considered among the younger composers, since his early life was passed in a very different sphere of work — as a professor of ..."

^Charles Youmans -The Cambridge Companion to Richard Strauss 2010 p252 1139828525 "Far too many authors misstate Strauss's role in the initial phases of this crusade by making him the instigator, when in fact Hans Sommer was the intellectual father of the cause.48 it was only after Sommer had published an article on the issue in early 1898 and then sent a copy to Strauss..."